Japanese Patent No. 2951818 discloses a known ink tank provided in an ink jet printing apparatus to supply a liquid such as ink (simply referred to as “ink” below) to an ink jet print head that ejects the ink in order to print on a print medium. FIG. 13A shows an ink tank 501 as an example utilizing the above configuration.
In the ink tank 501, a housing 504 composed of a container 502 and a cover 503 is partitioned into two spaces using a partitioning wall 514 having a communication portion 509. One of the two spaces is an ink accommodating chamber 506 which is closed except for the communication portion 509 of the partitioning wall 514 and which directly houses ink 515. The other space is a negative pressure generating member accommodating chamber 505 that houses a negative pressure generating member 511.
The ink tank 501 is detachably installed on a carriage (not shown) in an ink jet printing apparatus main body by using a lever 520; the carriage is reciprocated. An ink supply port 510 is formed in a bottom wall surface forming the negative pressure generating member accommodating chamber 505; an ink lead-out member 1203 is placed in the ink supply port 510 to supply the ink to an ink jet print head portion (not shown) supported on the carriage together with the ink tank 501. Further, an air communication port 508 is formed in a part of the cover 503 which forms a top wall surface of the negative pressure generating member housing chamber 505; the air communication port 508 is used to lead the air into the ink tank 501 as the ink 515 is led out. A gas introduction groove 519 is formed in an inner wall surface of the partitioning wall 514; the gas introduction groove 519 extends upward from an upper end of the communication portion 509.
The ink 515 is held in the negative pressure generating member housing chamber 505 by being absorbed by the negative pressure generating member 511. If an upper end of the gas introduction groove 519 is below the boundary between an area in which the ink 515 is held in the negative pressure generating member 511 and an area into which the air has entered, that is, below a gas/liquid interface, the air is introduced through the air communication port 508 as the ink is led out of the ink supply port 510. This lowers the gas/liquid interface.
Once the gas/liquid interface 511a lowers and reaches the upper end of the gas introduction groove 519 as the ink is consumed, air is introduced into the negative pressure generating member housing chamber 505 through the air communication port 508, and then the air enters the ink accommodating chamber 506 through the gas introduction groove 519 and communication portion 509 in the partitioning wall 514. Instead, the ink 515 from the ink accommodating chamber 6 is introduced into the negative pressure generating member housing chamber 505 through the communication portion 509 in the partitioning wall 514. This is called a gas and liquid exchanging operation; in this operation, air and the ink are exchanged between the negative pressure member housing chamber 505 and the ink accommodating chamber 506. In the gas and liquid exchanging operation, the gas introduction groove 519 serves to promote the introduction of the air from the negative pressure generating member housing chamber 505 into the ink accommodating chamber 506.
With the gas and liquid exchanging operation, even though the ink is consumed by the print head, an amount of ink equal to the amount of ink consumed is introduced into negative pressure generating member 11. Accordingly, the negative pressure generating member 11 is kept holding an approximately constant amount of ink. The gas/liquid interface 511a is thus maintained almost at the illustrated position. This allows the ink to be stably supplied to the print head, thus maintaining an almost constant negative pressure required to hold ink meniscus formed at ink ejection openings in the print head.
Another known configuration for adjusting the negative pressure on the ink in the ink tank is an ink accommodating chamber formed of a hard case and in which the ink is directly accommodated; as the ink is supplied to the print head, air (the atmosphere) from outside the ink tank is introduced directly into the ink accommodating chamber. With this configuration, when the ink is led out of the ink accommodating chamber as ink is supplied to the print head, the pressure in the ink accommodating chamber lowers. The decrease in pressure is offset by the air introduced into the ink accommodating chamber. This suppresses an excessive increase in negative pressure, thus maintaining an appropriate negative pressure.
The following advantages are given by the configuration in which the ink is accommodated directly in the ink accommodating chamber formed of the hard case: the efficiency with which the ink is accommodated can be increased, and almost all the accommodated ink can be used. On the other hand, the configuration shown in FIG. 13A utilizes the negative pressure generating member 511 to enable a more stable ink supply. This configuration further utilizes the ink accommodating chamber in which the ink is directly accommodated to enable an increase in the efficiency with which the ink is accommodated and used.
In either case, the ink tank used in the ink jet printing apparatus generally has a finite amount of ink accommodated and is configured to be detachable from the printing apparatus. When the ink is consumed up, the ink tank is replaced with a new one.
Desirably, the replacement of the ink tank is appropriately carried out when the ink in the ink tank is used up. Thus, the ink jet printing apparatus may be provided with an arrangement that determines the amount of ink remaining in the ink tank in order to notify the user of the appropriate time to replace the ink tank with a new one or to prevent a printing operation from being performed when the ink is exhausted. A known example of such an arrangement is a mechanism provided in the ink tank to detect that the ink remaining amount has reached a predetermined value. Various arrangements serving as such a detecting mechanism have been proposed and put to practical use.
In the configuration shown in FIG. 13A, an optical reflector 513 is provided at the bottom of the ink accommodating chamber 506 as means for detecting that the ink remaining amount has reached a predetermined value. The optical reflector 513 is composed of a material having a refractive index similar to that of the ink. As shown in FIGS. 13B and 13C, the optical reflector 513 is shaped like a prism with a vertical angle of 90°. In the printing apparatus main body, an optical module 551 having a light emitting section 552 and a light receiving section 553 is placed opposite the optical reflector 513. In this configuration, as shown by reference numeral 560, the light emitting section 552 irradiates the bottom of the ink accommodating chamber 506 with light. The light is transmitted through the bottom and is incident on a surface of the optical reflector 513 which has an inclination of 45° and which faces the interior of the ink accommodating chamber 506. When the ink accommodating chamber 506 contains a sufficient amount of ink, most of the thus incident light is refracted and then enters the ink accommodating chamber 506 as shown by reference numeral 561. Therefore, on this occasion, the light receiving section 553 detects little light. On the other hand, when the amount of ink in the ink accommodating chamber 506 decreases, such as to a level shown at 521, the light emitting section 552 irradiates the ink accommodating chamber 506 with light while the faces of the optical reflector 513 which face the interior of the ink accommodating chamber 506 are not in contact with the ink. Then, as shown by reference numerals 562 and 563, most of the applied light is reflected by the two 45° inclined surfaces of the optical reflector 513 which face the interior of the ink accommodating chamber 506. The light is then led to the light receiving section 553. In this manner, it is possible to determine whether or not the level of the ink in the ink accommodating chamber 506 has lowered to such a degree that the optical reflector 513 is exposed, on the basis of the quantity of light detected by the light receiving section 553.
Mechanisms that optically detect that the ink remaining amount has reached a predetermined value are disclosed in Japanese Patent Publication No. 3397441 and Japanese Patent Laid-Open Publication No. 2000-190520. Besides the mechanism using light, the following are known: a mechanism in which a pair of electrodes are provided in the ink tank so that detection is executed on the basis of a variation in the electric conductivity of the ink between the electrodes and a mechanism that executes detection on the basis of a variation in electrode capacitance generated between the ink tank and an electrode provided outside.
In any case, the mechanism determines whether or not the level of the ink has become equal to or lower than a certain height. If a single mechanism is provided, it is often placed on or near the bottom surface. Further, a configuration is also known in which a plurality of such mechanisms are provided so as to detect the level of the remaining ink and thus the amount of ink at multiple levels. Alternatively, it is possible to combine plural types of such mechanisms together to detect the ink remaining amount at multiple levels.
Another configuration that determines the amount of ink in the ink tank is a dot count method of using, for example, a control section of an ink jet printing apparatus to count the amount of ink consumed by a printing operation or the like after the ink tank has been installed, to estimate the amount of ink remaining in the ink tank. This configuration is also known to combine with a configuration in which the ink tank is provided with the above mechanism for detecting the amount of ink remaining in the ink tank.
Further, the above detachable ink tank is known to include a mechanical ID structure or bar code label indicating information such as the type of the ink tank or electric information storing means (ROM or the like) in order to, for example, prevent erroneous installation.